Upper bearing support assembly for internal turret

ABSTRACT

A turret mooring system for a vessel which includes a moon pool comprises a turret which is positioned in the moon pool, a buoy and anchor chain assembly for anchoring the turret to the sea floor, a bearing assembly for rotatably connecting the turret to the vessel, and a bearing support assembly which comprises an upper ring member to which the bearing assembly is connected, a lower ring member which is connected to the vessel in the moon pool, and a number of elongated support beams which are connected between the upper and lower ring members. In addition, the lower ring member is connected to the vessel near the vertical center of the vessel in order to minimize the deflections of the bearing assembly due to hogging and sagging of the vessel.

[0001] This application is based on U.S. Provisional Patent ApplicationNo. 60/465,092, which was filed on Apr. 23, 2003.

BACKGROUND OF THE INVENTION

[0002] The present invention is directed to a turret mooring systemwhich comprises a turret that is rotatably supported in the moon pool ofa vessel by at least an upper bearing assembly. More particularly, theinvention is directed to a bearing support assembly which isolates theupper bearing assembly from deflections of the vessel.

[0003] Turret mooring systems are commonly used to anchor a vessel tothe sea floor. Internal turret mooring systems typically comprise aturret which is rotatably supported in a moon pool that is formed in thehull of the vessel between the bow and the stern. The turret is oftensupported by both an upper bearing assembly which is connected betweenthe upper end of the turret and the top of the moon pool and a lowerbearing assembly which is connected between the lower end of the turretand the bottom of the moon pool. The upper bearing assembly typicallycomprises a combination axial and radial bearing which is capable oftransmitting both the vertical and horizontal mooring loads from theturret to the vessel. The lower bearing assembly usually comprises aradial bearing which transmits only the horizontal mooring loads fromthe turret to the vessel.

[0004] A vessel in the open sea is often affected by waves and swellswhich can cause the vessel to hog and sag. As the vessel hogs and sags,the normally circular cross section of the moon pool deflects intoalternating oval configurations. Since the vessel reacts somewhat like abeam in bending, these deflections are greatest at the top of the moonpool, which is normally where the upper bearing assembly is connected.In addition, turret mooring systems are typically designed to provide aclearance between the lower bearing assembly and the turret. As aresult, the horizontal mooring loads will cause the turret to pivotabout a horizontal axis located near the upper bearing assembly. Unlessmeans are provided to isolate the upper bearing assembly from thedeflections of the moon pool and the pivoting of the turret, thesedisplacements may damage the upper bearing assembly and interfere withthe operation of the turret mooring system.

[0005] In certain prior art turret mooring systems, bearing supportassemblies comprising elastomeric or steel springs have been employed toisolate the upper bearing assembly from the deflections of the moon pooland to allow the turret to pivot about a horizontal axis. However, thesebearing support assemblies contain many parts, require frequentmaintenance and are expensive.

SUMMARY OF THE INVENTION

[0006] In accordance with the present invention, these and otherdisadvantages in the prior art are overcome by providing a bearingsupport assembly for a turret mooring system which comprises a turretthat is rotatably supported in a moon pool of a vessel by an upperbearing assembly which is secured to an upper portion of the turret. Thebearing support assembly comprises an upper ring which is connected tothe upper bearing assembly, a lower ring which is connected to the moonpool, and a number of support beams which extend between the upper andlower rings. Furthermore, the lower ring is located near the verticalcenter of the moon pool where the deflections due to hogging and saggingof the vessel are minimal. In addition, the support beams are preferablydesigned to deflect slightly and thereby allow the turret to pivot abouta horizontal axis located near the upper bearing assembly.

[0007] Since the lower ring of the upper bearing support assembly islocated near the vertical center of the vessel, only minimal deflectionsof the vessel will be transmitted to the upper bearing assembly throughthe support beams. In addition, because the support beams will deflectand allow the turret to pivot, the pivoting of the turret will notadversely affect the upper bearing assembly. Thus, the upper bearingsupport assembly of the present invention provides an effective means toisolate the upper bearing assembly from both the deflections of thevessel and the pivoting of the turret.

[0008] These and other objects and advantages of the present inventionwill be made apparent from the following detailed description, withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 is a cross sectional view of a turret mooring system whichcomprises the upper bearing support assembly of the present invention;and

[0010]FIG. 2 is an enlarged cross sectional view of the upper bearingsupport assembly shown in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Referring to FIG. 1, the upper bearing support assembly of thepresent invention, which is indicated generally by reference number 10,is shown installed in an exemplary turret mooring system 12 for a vessel14. The turret mooring system 12 comprises a turret 16 which is mountedin a moon pool 18 that is formed in the hull 20 of the vessel 14. Theturret 16 may be secured to a disconnectable buoy 22 which in turn isanchored to the sea floor using a number of mooring chains 24. In use,the buoy 22 is hoisted from a submerged position to the turret 16 usinga pull-in rope 26 that is attached to a hoist 28, and the buoy isconnected to the turret with a conventional structural collet connector30.

[0012] The turret 16 is rotatably supported in the moon pool 18 by anupper bearing assembly 32 and, when the buoy 22 is attached to theturret, a lower bearing assembly 34. In this manner, the vessel 14 isallowed to weathervane around the turret 16 while still being firmlyanchored to the sea floor. The upper bearing assembly 32 ideallycomprises a combination thrust and radial bearing, such as aconventional three-row roller bearing, which supports the weight of theturret 16 and the mooring chains 24 and accommodates the horizontal andvertical mooring loads acting between the turret and the hull 20. Thelower bearing assembly 34, in contrast, preferably comprises a radialbearing which accommodates only the horizontal loads acting between thebuoy 22 and the hull 20. If desired, the turret mooring system 12 mayalso include a number of bumper pads 36, which may be comprised of, forexample, rubber or polyethylene, to cushion the lower portion of theturret 16 from the hull 20 prior to connecting the buoy 22 to theturret.

[0013] In accordance with the present invention, the upper bearingassembly 32 is supported on the bearing support assembly 10. Referringto FIG. 2, the bearing support assembly 10 comprises an annular upperring 38 to which the upper bearing assembly 32 is connected, an annularlower ring 40 which is connected to the hull 20, and a number ofelongated support beams 42 which are each secured between the upper andlower rings. In a preferred embodiment of the invention, the bearingsupport assembly 10 is a pre-fabricated metal structure, that is, theupper ring 38, the lower ring 40 and the support beams 42 are allconstructed of a suitable metal, such as carbon steel, and securedtogether such as by welding prior to being installed in the moon pool18.

[0014] In the illustrated embodiment of the invention, the upper ring 38is secured to the upper portion of the turret 16 and the support beams42 are sufficiently long to allow the lower ring 40 to be secured to thehull 20 near the vertical center of the vessel 14. At this position, thedeflections of the lower ring 40 caused by hogging and sagging of thevessel 14 will be significantly reduced compared with the deflectionsthe lower ring would experience if it were secured to the hull 20 closerto the upper ring 38. As a result, the upper ring 38 will alsoexperience reduced deflections, and the upper bearing assembly 32 willtherefore remain generally circular. Thus, it may be seen that thebearing support assembly tends to isolate the upper bearing assembly 32from the distortions of the moon pool 18 which are caused by hogging andsagging of the vessel 14.

[0015] The length, number and cross sectional configuration of thesupport beams 42 will depend on the size of the turret 16 and theanticipated vertical mooring loads that will be transmitted through theupper bearing assembly 32. In addition, the length and cross sectionalconfiguration of the support beams 42 are selected so that they willdeflect slightly to allow the turret 16 to pivot about a horizontal axislocated near the upper bearing assembly 32 when the turret is subjectedto horizontal mooring loads. In an exemplary embodiment of theinvention, for example, the support beams 42 may each be constructed oftwelve-inch diameter carbon steel tubing and have a length ofapproximately twenty feet, and a total of twenty four such support beamsmay be evenly distributed around the bearing support assembly 10.

[0016] Referring still to FIG. 2, the upper ring 38 preferably comprisesa circular base 44 which is attached to the top of a cylindrical hoop46. In addition, the upper end of each support beam 42 is ideallyattached to an upper rib 48 which optimally is connected to both thebase 44 and the hoop 46. The upper ring 38 may also comprise a stiffenerring 50, which is preferably attached to the bottom of the hoop 46 andeach upper rib 48, to facilitate the assembly of and provide additionalstiffness to the upper ring.

[0017] If as shown in FIG. 2 the upper bearing assembly 32 comprises athree-row roller bearing, a lower or outer race 52 of the bearingassembly may be bolted to the base 44 and an upper or inner race 54 ofthe bearing assembly may be attached to a conventional upper bearingring 56 which is connected to or formed integrally with the upper end ofthe turret 16. Thus, the vertical and horizontal mooring loads which acton the turret 16 will be transmitted through the upper bearing assembly32 to the upper ring 38, from the upper ring to the support beams 42,and from the support beams to the lower ring 40.

[0018] The lower ring 40 preferably comprises a circular reaction ring58 and a number of lower ribs 60, each of which is secured to thereaction ring and to the lower end of a corresponding support beam 42.The reaction ring 58 is supported on a conventional moon pool supportring 62 which is attached to the moon pool 18 near the vertical centerof the vessel 14. In addition, the bearing support assembly 10 ideallyincludes a number of radial and axial jack screws 64 and 66,respectively, which are operatively engaged between the hull 20 and/orthe support ring 62 on the one hand and the reaction ring 58 on theother hand, to provide a means for aligning the axis of rotation of theupper bearing assembly 32 with the axis of rotation of the lower bearingassembly 34. Once the axes of rotation are properly aligned, theinterface between the support ring 62 and the reaction ring 58 may befilled with grout and these two components secured together with, forexample, a number of bolts 68 to prevent the separation of the bearingsupport assembly 10 from the moon pool 18 due to uplift of the turret16.

[0019] In operation of the bearing support assembly 10, the vertical andhorizontal mooring loads acting on the turret 16 are transmitted throughthe upper bearing assembly 32 to the upper ring 38. From the upper ring38, the mooring loads are transmitted through the support beams 42 tothe lower ring 40, and from the lower ring 40 to the hull 20 of thevessel 14. In addition, due to the clearance between the turret 16 andthe lower bearing assembly 34, the horizontal mooring loads will causethe turret to pivot about a horizontal axis located near the upperbearing assembly 32. The resulting bending force will be transmittedthrough the upper bearing assembly 32 to the support beams 42, whichwill deflect slightly to allow the turret 16 to pivot.

[0020] Since the vessel 14 reacts somewhat like a beam in bending, thedeflections of the normally circular shape of the moon pool 18 caused byhogging and sagging of the vessel 14 will be minimized near the verticalcenter of the hull 20. Thus, by mounting the lower ring 40 near thevertical center of the hull 20, the deflections of the lower ring due tohogging and sagging of the vessel 14 will also be minimized. As aresult, the upper ring 38 and, thus, the upper bearing assembly 32 willremain relatively circular during operation. In addition, due to theparticular construction of the support beams 42, they will deflectslightly to accommodate the pivoting of the turret 16 caused by thehorizontal mooring loads and thereby prevent the upper bearing assembly32 from becoming damaged. Therefore, the bearing support assembly 10effectively isolates the upper bearing assembly 32 from both thedeflections of the vessel 14 and the pivoting of the turret 16.

[0021] It should be recognized that, while the present invention hasbeen described in relation to the preferred embodiments thereof, thoseskilled in the art may develop a wide variation of structural andoperational details without departing from the principles of theinvention. Therefore, the present application should be construed tocover all equivalents falling within the true scope and spirit of theinvention.

What is claimed is:
 1. A turret mooring system for a vessel whichincludes a moon pool, the turret mooring system comprising: a turretwhich is positioned in the moon pool; means for anchoring the turret tothe sea floor; a bearing assembly for rotatably connecting the turret tothe vessel; and a bearing support assembly which comprises an upper ringmember to which the bearing assembly is connected, a lower ring memberwhich is connected to the vessel in the moon pool, and a number ofelongated support beams which are connected between the upper and lowerring members; wherein the lower ring member is connected to the vesselnear the vertical center of the vessel.
 2. The turret mooring system ofclaim 1, wherein the support beams are designed to deflect in order toallow the turret to pivot about a horizontal axis located near thebearing assembly.
 3. The turret mooring system of claim 1, wherein theupper ring member comprises a circular base to which the bearingassembly is connected and a cylindrical hoop which is connected to thebase.
 4. The turret mooring system of claim 3, wherein the upper ringmember further comprises a number of upper ribs, each of which isconnected to the base, the hoop and an upper end of a correspondingsupport beam.
 5. The turret mooring system of claim 1, wherein the lowerring member comprises a circular reaction ring which is supported on acorresponding portion of the vessel.
 6. The turret mooring system ofclaim 5, wherein the lower ring member further comprises a number oflower ribs, each of which is connected to the reaction ring and a lowerend of a corresponding support beam.
 7. The turret mooring system ofclaim 5, wherein the reaction ring is supported on a support ring thatis attached to the vessel.
 8. The turret mooring system of claim 7,further comprising means for aligning the axis of rotation of thebearing assembly with another axis.
 9. The turret mooring system ofclaim 8, wherein the aligning means comprises a number of axial jackscrews which are operatively engaged between the support ring and thereaction ring.
 10. The turret mooring system of claim 9, wherein thealigning means further comprises a number of radial jack screws whichare operatively engaged between the vessel and the reaction ring. 11.The turret mooring system of claim 7, further comprising means forsecuring the reaction ring to the support ring.
 12. The turret mooringsystem of claim 11, wherein the securing means comprises a number ofbolts.
 13. The turret mooring system of claim 7, further comprising ahardenable grout which is disposed between the support ring and thereaction ring.
 14. A turret mooring system for a vessel which includes amoon pool, the turret mooring system comprising: a turret which ispositioned in the moon pool; means for anchoring the turret to the seafloor; a bearing assembly for rotatably connecting the turret to thevessel; and a bearing support assembly which comprises an upper ringmember to which the bearing assembly is connected, a lower ring memberwhich is connected to the vessel in the moon pool, and a number ofelongated support beams which are connected between the upper and lowerring members; wherein the upper ring member is located near a firstvertical position of the moon pool, the lower ring member is locatednear a second vertical position of the moon pool, and the deflections ofthe moon pool due to hogging and sagging of the vessel are smaller atthe second vertical position than at the first vertical position. 15.The turret mooring system of claim 14, wherein the second verticalposition is located near the vertical center of the vessel.
 16. Theturret mooring system of claim 14, wherein the support beams aredesigned to deflect in order to allow the turret to pivot about ahorizontal axis located near the bearing assembly.
 17. The turretmooring system of claim 14, wherein the upper ring member comprises acircular base to which the bearing assembly is connected and acylindrical hoop which is connected to the base.
 18. The turret mooringsystem of claim 17, wherein the upper ring member further comprises anumber of upper ribs, each of which is connected to the base, the hoopand an upper end of a corresponding support beam.
 19. The turret mooringsystem of claim 14, wherein the lower ring member comprises a circularreaction ring which is supported on a corresponding portion of thevessel.
 20. The turret mooring system of claim 19, wherein the lowerring member further comprises a number of lower ribs, each of which isconnected to the reaction ring and a lower end of a correspondingsupport beam.
 21. The turret mooring system of claim 19, wherein thereaction ring is supported on a support ring that is attached to thevessel.
 22. The turret mooring system of claim 21, further comprisingmeans for aligning the axis of rotation of the bearing assembly withanother axis.
 23. The turret mooring system of claim 22, wherein thealigning means comprises a number of axial jack screws which areoperatively engaged between the support ring and the reaction ring. 24.The turret mooring system of claim 23, wherein the aligning meansfurther comprises a number of radial jack screws which are operativelyengaged between the vessel and the reaction ring.
 25. The turret mooringsystem of claim 21, further comprising means for securing the reactionring to the support ring.
 26. The turret mooring system of claim 25,wherein the securing means comprises a number of bolts.
 27. The turretmooring system of claim 21, further comprising a hardenable grout whichis disposed between the support ring and the reaction ring.
 28. Abearing support assembly for a turret mooring system which includes aturret that is positioned in a moon pool of a vessel and is rotatablyconnected to the vessel by a bearing assembly, the bearing supportassembly comprising: an upper ring member to which the bearing assemblyis connected; a lower ring member which is connected to the vessel inthe moon pool; and a number of elongated support beams which areconnected between the upper and lower ring members; wherein the lowerring member is located closer to the vertical center of the vessel thanto the top of the moon pool.
 29. The turret mooring system of claim 28,wherein the lower ring member is connected to the vessel near thevertical center of the vessel.
 30. The turret mooring system of claim28, wherein the support beams are designed to deflect in order to allowthe turret to pivot about a horizontal axis located near the bearingassembly.
 31. The turret mooring system of claim 28, wherein the upperring member comprises a circular base to which the bearing assembly isconnected and a cylindrical hoop which is connected to the base.
 32. Theturret mooring system of claim 31, wherein the upper ring member furthercomprises a number of upper ribs, each of which is connected to thebase, the hoop and an upper end of a corresponding support beam.
 33. Theturret mooring system of claim 28, wherein the lower ring membercomprises a circular reaction ring which is supported on a correspondingportion of the vessel.
 34. The turret mooring system of claim 33,wherein the lower ring member further comprises a number of lower ribs,each of which is connected to the reaction ring and a lower end of acorresponding support beam.
 35. The turret mooring system of claim 33,wherein the reaction ring is supported on a support ring that isattached to the vessel.
 36. The turret mooring system of claim 35,further comprising means for aligning the axis of rotation of thebearing assembly with another axis.
 37. The turret mooring system ofclaim 36, wherein the aligning means comprises a number of axial jackscrews which are operatively engaged between the support ring and thereaction ring.
 38. The turret mooring system of claim 37, wherein thealigning means further comprises a number of radial jack screws whichare operatively engaged between the vessel and the reaction ring. 39.The turret mooring system of claim 35, further comprising means forsecuring the reaction ring to the support ring.
 40. The turret mooringsystem of claim 39, wherein the securing means comprises a number ofbolts.